Validate phone number with JavaScript

Question

I found this code in some website, and it works perfectly. It validates that the phone number is in one of these formats:
(123) 456-7890 or 123-

Answer 1

I would suggest using something clearer (especially thinking to who will have to maintain the code)... what about:

var formats = "(999)999-9999|999-999-9999|9999999999";
var r = RegExp("^(" +
               formats
                 .replace(/([\(\)])/g, "\\$1")
                 .replace(/9/g,"\\d") +
               ")$");

where the regexp is built from a clear template ? Adding a new one would then be a no-brainer and may be even the customer itself could be able to do that in a "options" page.